Field-effect transistors include source, drain and gate structures. A biasing voltage applied across gate and source terminals allows the flow of charge carriers, namely electrons or holes, between source and drain. Tunneling field-effect transistors (TFETs) are characterized by oppositely doped source and drain regions. Band-to-band tunneling is caused upon application of a sufficient gate bias. TFET structures including strained Ge/SiGe heterojunctions on silicon as well as those based on group III-V materials have been disclosed.
Tunneling field-effect transistors are of interest for low-power operations due to their potential to achieve a sub-60 mV/decade subthreshold slope. A broken-gap heterojunction source is employed to achieve such a steep subthreshold slope in some TFETs.